This invention relates to the coking of residual oil, and the partial gasification and desulfurization of coal, and more particularly, to performing these operations simultaneously in a single reactor.
Residual petroleum oil fractions produced by atmospheric or vacuum distillation of crude petroleum are characterized by a relatively high metals content. This occurs because substantially all of the metals present in the original crude remain in the residual fraction. Principal metal contaminants are nickel and vanadium, with iron and small amounts of copper sometimes being present.
The high metals content of the residual fractions generally preclude their effective use as chargestocks for subsequent catalytic processing, such as catalytic cracking and hydrocracking, because the metal contaminants deposit on the special catalysts for these processes and cause the formation of inordinate amounts of coke, dry gas, and hydrogen.
It is current practice to upgrade certain residual fractions by a pyrolytic operation known as coking. In this operation the residuum is destructively distilled to produce distillates of low metals content and leave behind a solid coke fraction that contains most of the metals. Coking is typically carried out in a reactor or drum operated at about 800.degree.-1100.degree. F. temperature and a pressure of 1-10 atmospheres. The economic value of the coke byproduct is determined by its quality, particularly its sulfur and metals content. Excessively high levels of these contaminants make the coke useful only as lowvalued fuel. In contrast, cokes of low metals content, for example up to about 100 ppm (parts per million by weight) of nickel and vanadium and containing less than about 2 wt.% sulfur, may be used in high valued metallurgical, electrical, and mechanical applications.
Typical coking processes are shown in "PETROLEUM PROCESSING-PRINCIPLES AND APPLICATIONS", R. J. Hengstbeck, McGraw Hill Book Co., Inc., 1959, p. 138. Delayed coking is a batch process which is expensive to operate because of its high labor intensity. The liquid yield is not as high as it could be due to excessive secondary cracking. Fluid coking is a continuous process. The liquid yield is higher but it produces coke of low value. Transferring coke between the burner and the reactor is expensive.
As petroleum resources become increasingly scarce, conversion of coal into gas and liquid fuels becomes increasingly necessary. Currently many such processes are at various stages of development. Unfortunately, the processes are all expensive, mainly due to their high investment costs. The current challenge in process development is to lower the investment cost.
From coal, substantial amounts of gas and liquid fuels can be obtained by pyrolysis and partial gasification. FIGS. 20.52, 24.14, 24.33, 24.37, 24.38, and 24.39 of "Chemistry of Coal Utilization," National Research Council Committee on Chemical Utilization of Coal, H. H. Lowry, Chairman and Editor, New York, Wiley, 1945 show typical reactors for gasification of coal including the synthane gasifier, the Battelle-Union Carbide gasifier, the British Gas-Lurgi slagging gasifier, the U.S. Bureau of Mines three-stage coal gasifier-combustor, and the West Virginia University pyrolizer/gasifier.
U.S. Pat. No. 4,317,711-Yan describes a method for co-processing residual oil and coal by visbreaking a slurry of heavy hydrocarbon oil and finally divided coal. The visbroken mixture yields a demetalized liquid hydrocarbon product. "COAL AS LIQUID FUEL EXTENDER FOR PROCESS HEATERS", Ser. No. 346, 436, filed Feb. 8, 1982, Yan, describes a process in which a slurry of coal and residual oil is visbroken to yield liquid product which is suitable for use in process heaters and solid fuel which is suitable for use in solid fuel furnaces.
The use of coal as a refinery fuel is becoming increasingly desirable. However, it is quite difficult to use coal for process heaters. Coal gasification is one way of converting coal to a fuel which can be used in these heaters. However, maintaining a devoted gasifier for the generation of gaseous fuel for refinery use is quite expensive because of its small size and the need for an oxygen plant. The refinery power plant can use solid fuels, but the sulfur content of coal and coke are often too high. Markets exist for low sulfur coke and coal as carbon material for fuel. However, the desulfurization of solid coke or coal is difficult, because it is impractical to calcite these solid fuels to 1800.degree. F. or higher which is required to thermally volatize sulfur compounds.
It is an object of the present invention to upgrade residual oil by coking it while simultaneously devolatizing and partially gasifying coal or coke to produce fuel gas, coal liquid and low sulfur char.
It is another object of the present invention to desulfurize the coal to low sulfur, high heating value solid fuel.